1. Field of Invention
This invention relates to ceramic cements and specifically to a new phosphate glass cement for hard tissue surgical implants and prostheses for man and animals in the dental, medical and veterinarian fields.
2. Description of Prior Art
In dental and medical practice, several different ceramic and glass materials are used for bone grafts and other prosthetic applications. These mainly contain calcium and phosphorus, the elements present in the mineralized tissue of bone and teeth.
Heretofore, some of these prosthetic ceramic materials set up and harden as a true cement whereas others are powder which when mixed with an aqueous media to form suspensions or pastes do not harden.
One such prosthetic material is Plaster of Paris powder, which upon mixing with water is placed in bony defects, thereupon hardening. Beginning in the 1800's and still in limited use today, this substance of CaSO.sub.4.2H.sub.2 O is resorbed by the body but is unpredictable as to its efficacy in stimulating bone to heal normally.
A second ceramic bone graft substance is an organic bone, that is, bovine bone with the organic components removed to leave the calcium phosphate mineral powder, essentially an apatite, Ca.sub.5 (PO.sub.4,CO.sub.3).sub.3 (OH). It becomes a paste when mixed with water but not a cement with the disadvantage the particles can migrate and wash out from the implant site.
A third bone graft material is of synthetic calcium phosphate apatite in the U.S. Pat. No. 4,097,935 to M. Jarcho, 1978 Jul. 4. Used as a coarse powder paste without hardening, the material can migrate from the site and is not considered biodegradable although a more recent form of apatite called OsteoGen of Impladent, Inc. is regarded as resorbable.
A fourth ceramic graft in the U.S. Pat. No. 3,913,229 to T. Driskell and others, 1975 Oct. 21 , is a non-apatite powder called tricalcium phosphate, Ca.sub.3 (PO.sub.4).sub.2 used as a paste. This substance is biodegradable but is not a cement.
Prosthetic cements made of various calcium phosphate powders and an aqueous reacting liquid were recently reported. H. Morima and others in the journal Gypsum Lime, 188 11-16 (1984) made a cement of alpha-Ca.sub.3 (PO.sub.4).sub.2 powder. In the patent JP 59,182,263, 1984 Oct. 17, Ca.sub.3 (PO.sub.4).sub.2 cements that solidify with 4N HNO.sub.3 were proposed for the repair of bones and teeth. W. Brown and L. Chow in U.S. Pat. No. 4,518,430, 1985 May 21,invented bone and tooth prosthetic cements from various calcium phosphate powders such as CaHPO.sub.4.2H.sub.2 O and Ca.sub.8 (PO.sub.4).sub.2 O mixed with acidic or basic water solutions.
In addition to the crystalline calcium phosphate and calcium sulfate bone graft ceramics listed above, there are several biologically compatible glasses containing calcium and phosphorus used as a non-cement prosthetic bone material. The best known of these is called Bioglass which is basically a silicate glass and non-resorbable with applications as coating on metals or as a solid bone prosthesis.
A more recent prosthetic glass based on a phosphate rather than silicate composition and containing CaO and other cations in the patent Appl. GB 2,178,422 to C. Drake, 1987 Feb. 11, is a dissolvable implant, but not a cement.
Besides the phosphate-containing implant glasses, none of which are cement systems, there do exist glass cements for the purpose of dental restorations, but not for surgical implants or bone grafting. The oldest of these is the so called silicate cement used for anterior tooth filling first introduced in the late 1800's of obscure origin. It is a silicate glass powder including ions of calcium, aluminum, sodium, and fluorine which when reacted with water solution of phosphoric acid hardens into a translucent cement. A more recent and dentally important modification of the silicate cement is the so called glass ionomer cement patented by A. Wilson and B. Kent, Ger 2,061,513 in 1971 June 24. This ionomer glass uses a silicate glass powder very similar to the silicate cement, but reacts the powder with an aqueous solution of polyacrylic acid or a copolymer of acrylic and itaconic acids. W. Potter and others invented a modification of the ionomer cement by using a reacting solution of polycarboxylic acid in the U.S. Pat. No. 4,123,416 of 1978 Oct. 31.